AIRBRAKES 101: 10 levels of TRAIN BRAKE understanding!
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- Опубліковано 6 чер 2024
- In this video, we look at an overview to how air brakes work on trains, for an audience that knows nothing about them. I know that you air brake gurus out there will notice things like me not even discussing the equalizing reservoir or not talking into too many nuances, but I wanted to ensure that someone who isn't too familiar could get to a good level of understanding how things work generally... we'll nerd out down the road :)
Sorry about the darn audio quality in the beginning again. I know what the problem is, unfortunately it's not an easy fix. Long story short, don't buy anything from Universal Audio if you use Windows.
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0:00 Intro
1:29 L1: Air, piston, shoe.
3:27 L2: Air compressors
5:20 L3: Straight Air (independent brakes, old train brakes)
7:24 L4: Automatic Air
12:37 L5: Brake rigging
15:26 L6: Non-self lapping automatic brake valves
22:00 L7: Self-lapping automatic brake valves
24:15 L8: Car control valves
27:55 L9: Doubleheading, Diesel MU controls
34:07 L10: Positive Train Control (PTC) Airbrake Interface
38:05 Recap & Outro
Engineer Ralph Harty had the distinction of two major derailments with the same train on the Brooten Line in the 70's. (Superior, WI to Glenwood, MN, 200 miles total..) I believe this was what encouraged the rail defect use on that line. They ran the rail detector over the Brooten Line (Moose Lake, MN to Brooten, MN portion of the line. 80 pound rail.) the rail from Moose Lake to Brooten averaged twenty-two defect to the mile. This was back in the 1970's. They ran out of replacement rail and bought rail from the BN that had been ripped up on a branch line. Rail profile was almost the same, with the exception it was a quarter of an inch higher. That, along with the line not having seen a tamper in years was not entirely a pleasure to ride over. With all the low rail joints, rocking back and forth latterly, and the mismatched rail you needed to wedge yourself between the seat and the wall. Going over the rail joint your teeth would chatter if you didn't sit slack-jawed. The Roadmaster didn't want three axle locomotives on it either.
Although I did have six three-axle 3,000 HP locomotives once with one hundred empty grain cars to Glenwood. There was a ten MPH speed restriction over the Kettle River. When the green flag was called out by the conductor I was at a whistle post for a crossing. Every time I advanced the throttle a notch, you could feel the train lurch ahead. All six units were on line. I was only able to get throttle six of eight notches when I went over the crossing at forty mph, track speed. Not bad for 10 to 40 in 1,320 feet with 100 cars.
With all this bad rail the speed on the Brooten Line was dropped from 35 to 10mph from Moose Lake to Brooten, about one hundred thirty five miles, with a whole slew of slow orders of 5mph. Twenty-eight of them at five mph. I would line the slow orders up on a clipboard I brought with and tear them off as I exited each one. Trains were usually 120 cars both ways at that time. It took two days to get to Glenwood and two days to get back. The halfway layover was Onamia, MN. Setting the train brakes in some of these slow orders going East with loaded grain hopper to maintain five mph was down right tempting fate to keep the train in one piece with sixteen thousand plus ton trains. This is where I became creative with applications. On the engines with 26L with maintaining features I would ride the hump from the six pound den-tent. (This first hump from the running position is called the six pound notch). I didn't look at it, I would use my index finger to tell where it was at. This would be about a eight to nine pound reduction with a 90 pound train line. After exhaust ended I would release it counting seconds in my mind (One - one thousandth, two - one thousandth, etc.) and then resetting to the same amount again. Doing this multiple times with wait times between applications and additional seconds of release depending on speed, train length and track conditions. Soo Line ore cars had the old air brake equipment, the newer grain cars had an accelerated release if a ten pound or more application was made. What the accelerated release did was dump air from the emergency portion of the car air reservoir into the train line to propagate a faster release. Doing this set, release, and the set with ten or more pound applications was real tricky with the accelerated release, but it could be done. This kept the train stretched, even through shallow sags. I did this for twenty-four years and never tore a train apart. I even stretch braked ore trains this way when there was a 100 car limit. On longer ore trains I used forty retainers in the SD position (SD - Slow Direct) on the head end. Soo Line at that time did not have any engines with dynamic braking.
I image when cabooses were still used the hind end crew appreciated it. One trip with a Superior Engineer deadheading in the caboose from Dresser to Superior remarked to the Conductor why the slack wasn't running in or out anymore, his reply “The Fireman is running the Engine now”. I rode many a caboose and knew what it was like with different Engineers.
The worst stop while a Brakeman on the GN back in the sixties, was at Cohasset, MN. We had two hundred fifty empty forty foot box cars going West, and the speed was about twelve to fifteen miles per hour when a piece of scrap metal laying between the rails parted the air hoses between the engines. I was in the cupola at the time. Stop was about instant with the brakes in emergency at the head end first with the slack running in before the train line dynamited on the caboose. The four total caboose end windows shattered (two on each end), the back door, which opened inward, tore the lock hasp off, and was open, the coal stove was ripped off the floor with stove pipe flying all over, the large batteries in the cabinet went through the interior wall and the caboose being of wood construction, all the dust in the cracks was airborne with viability down to about five feet. Luckily I was partly braced, but did end up in the seat in front of me, uninjured.
On engines with 24rl or 6blc brake equipment using the feed valve or riding the release hump to maintain brake pipe pressure is what I used. Riding the release was not fully in release position choking off the air supply enough so as to maintain the brake pipe pressure at the pressure set during the application, this was the trickiest of procedures!!! The Soo 24rl valves didn't have the optional maintaining feature. (I believe these were repurposed off steam engines). On 26L Brake Valves when making applications it was actually referencing to a 100 cubic inch chamber in the brake valve itself. Sometimes you would get one that leaked down. That meant that the train line reduced also. I would watch for this during air tests. On long downgrades this was a problem. That's when you would use the feed valve. You would make the application, and when it equalized, you cut the brake valve out, moved the handle to running position, backed the feed valve off to match the current brake pipe pressure, then cut the valve back in. I don't think the railroad mechanical department thought too much of that procedure, although I did try dumping the air with the valve cut out and it did work on that one engine I tried it on. A 26L brake valve set for 90 psi train line equalizes at a 26 pound reduction, hence the name 26. Set for 75 psi it equalizes at about 21-22 psi reduction. 6Blc valves had a main reservoir pressure to the brake pipe position to the left of the running position. You had to be careful not to overcharge the brake pipe. If you did, brakes would stick on. This was a good way to have a accelerated release on the old air brake systems that didn't have the accelerated release built in. And NO, I never tore a train apart doing this during my twenty-four year career. Jack Peterson hogheaddotnet
Cheers Jack, I'd love to get a beer with ya and hear these stories in person. You can tell you did the thing for real, and you're proud of it. Thanks for the comment, and the stories :D
That's a freaking novel, hoss!
Not sure if it's adventure or horror, though. The first part had me groaning aloud, and the caboose part - Good Lord!
Interesting driving with a sustained min service application. That's nominally a 10# drop to just set the shoes, as you say. Makes good sense, and somehow you came up with that as a fireman?!?! That's some savvy.
Dynamic braking wouldn't have helped a bit unless you had DP in the back to mirror the lead DB. It might've saved some shoe wear.
Gotta get to work now. I'll read the rest of your nail-biter later!
Ok: I read further: I _think_ 24 RLs are vintage 1920s, + or -, probably -. That whole operation is starting to sound like Johnny Cash's Cadillac.
Seems like you made the best of it, which is great credit to you.
@Metra 212 Productions it depends on the railroad and their feed valve settings. We run at 70 at the museum. Some passenger is not 110. Yes for most larger ops you are correct these days it's 90 and 110 but that's not a hard and fast rule.
Yea i do the same on my H.o gauge train 🤓
I think your style of drawing it out, back of the napkin so to speak, lends itself well to getting people with no prior knowledge to understand what you’re talking about! It’s a great introduction to a very important concept, thank you so much for making these videos! 😁
These drawings are masterpieces compared to some of my professors, lmao. He's doing just fine, I agree.
These videos should probably be required training material for everyone coming into operations at railroad museums, they're very well done at building a basic understanding of how the systems actually work in a way I haven't been able to find yet outside of being on the trains themselves.
excellent explanation! i watched 44 minutes about a topic that will never be of any use to me in my life and i loved it. your simple drawings surprisingly work very well to get your points across
As a retired railroader I think your tutorial on air brakes was great. Strangely enough I was just going through an old Western House catalog on pre 1900s air brakes.And my favorite expression for putting a train into emergency is Wipe the Clock. 😁
Wipe the clock! I've only heard that once or twice. We usually say dynamite or big hole 'round my way. I appreciate the feedback, cheers :) hope you are enjoying retirement!
That sounds similar to the procedure of "Wiping The Dial" which was for the driver/engineer to drain the entire contents of the brake system out completely (while standing sill of course) and recharging with new air. This is to get ride of any water/dampness/condensation that accumulates in the system over time (after about a coupe of hours).
I am a train driver in Switzerland.
We know brakes and the techniques like the automatic brake too.
I think you explained the brakes perfectly. Good job!
Cheers!
The periodic recaps are *key* to what makes these videos so good. Makes it really easy to get back into the video after a distraction.
For 37 years I worked as a truck mechanic and I made a career change in '08. From then on I worked as a millwright in a steel mill. There I worked on overhead cranes. On weekends we had the responsibility for derailed trains so we were witnessing much of what you've described. Those poor guys driving locomotives were fired for derails. They would normally get the job back but wow. Through the years there I noticed that the brakes on trains were essentially bigger versions of truck systems. That is probably an oversimplified description of what I saw. I never was able to talk to someone knowledgeable about the train brakes on a mechanics level. The RTO (remote train operator) operators were always new and couldn't give much info. Your video has shined a light on some of the things I had been trying to put together about the systems.
Like I said about working on trucks I didn't really look into it much but the FMVSS manual for trucks also covered rail cars and locomotives.
Thanks for your video it's answered a few questions that I've had on the subject.
Fun Fact: The reason why all Class A trucks have airbrake systems in place are because of how successful it was to slow down heavy trains of any size.
No it because brake fluid boils with the extreme heat needed to slow anything with a weight above 20,000 pounds. Air just expands and applies more force in an air brake system.
@greyfox79007 if you are heating up the air in the break chambers enough for it to expand your vehicle is probably on fire at that point.....
@@katokagome4670 apart from the amount lost if a leak occurs, the break-cylinders on the rear wheels are also equipped with a spring, strong enough to very quickly overcome the atmospheric pressure and apply the breaks automatic in case of total air-system failure
the break-cylinders on the rear wheels are also equipped with a spring, strong enough to very quickly overcome the atmospheric pressure and apply the breaks automatic in case of total air-system failure.
at least were I work in Germany
@@katokagome4670 yeah boiling the breaks is bad...
ahhh nope bad doesn't cover the whole affair.
and in this case I refer to any and all ways to damage a break system to the point of inoperability:
# Glazing the pads
# leak of any kind
# busted caliper
you name it and there's gonna be at least 500 cars on the road at any given time that have this specific defect.
Finally. Someone who can explain how exactly the air system applies the brakes through a single hose by a reduction of pressure without springs. Tyvm.
I really appreciate these videos Mark. I’m a heavy equipment mechanic and Diesel engine specialist, I’m used to knowing how things work, I’ve always wondered the smaller inner workings of steam locos and trains in general. Thank you sir. Keep up the good work!
Very cool! I am glad that you enjoy these. I will probably be doing a diesel locomotive one soon enough :)
Much appreciate your lucid explanation. As a brakeman working as holiday relief one summer (CPR) I must have had to do some learning but have to thank you for correcting a misunderstanding of the brake system I've carried all these years. (How many years? Well, just a few years earlier I shoveled coal at least once on a tired yard engine in shunting service and thanks to UA-cam now also have a much clearer understanding of how injectors work).
It's so awesome how you break these down into 10 different levels. It let's people "tap out" after a certain point if they choose/need to.
more like brake these down eh
Absolutely loving this new series. Keep it up Hyce, you're the man.
I’m slowly worming my way through the 101 series and love it. I’ve always loved trains and knew a little about them but these videos have really added a whole new appreciation for the railroad. I’m looking forward to watching them all!
I watched your first "10 levels" video and have to say this one was equally informative. Thank you for making this, I learned a significant amount.
I really enjoyed this video. I look forwards to watching it again with my son, as me and him are currently each working on scale model railroad projects. really neat video. Thank you for taking the time on this one.
While freight car control valves are not designed to partially release there are a couple ways to trick them into making a lighter brake application, or what feels like a less than minimum application across the train.
1. If you have a relatively short train and have made a moderate to heavy brake application, release it and then make the same application again right away. If you time it right everything will settle out with the car control valves in the lap position once again before the brake cylinders finished exhausting, leaving you with a lighter brake application. But this is quite tricky, it requires a lot of practice to get right, and does not work as well on long trains where the head end cars may have completely released well before those on the tail end.
2. If you want a very light brake application, take a minimum and let it set, release it, and then take a minimum again when the flow drops below 40 CFM. Making a very light brake pipe reduction before the train is fully charged will have the effect of setting the brakes on some cars and not on others. It is important to note that doing this will create 'stickers' (cars that won't release normally), so when you are done with this brake you will have to 'clean it up' by making a heavy brake application and letting it set completely before releasing it (you need at least a 10 PSI rise to reliably get rid of stickers). We have a number of grades in the 0.5% to 1.2% range where dynamic braking alone won't hold the train, but a full minimum application is too much.
3. This is a variation on 2, if you want a really light brake you can take a minimum and then release it before it finished exhausting, this deliberately creates stickers so once again you'll have to 'clean it up' once you no longer need the brake.
In general these sort of strategies are called "Cycle Braking", and they take a fair amount of practice to get used to and get right. It is important to not abuse them, if you cycle brake too many times you can "pee away your air", and at worst you could reduce the brake pipe pressure to the the point where 'soaking it' will no longer propagate the emergency braking signal. You need at least 45 PSI in the brake pipe for this, and we are supposed to put it in emergency if the brake pipe gets down to 50, regardless of how we got to that unenviable position.
Cheers Bob, this is a brilliant comment. I've done #1 several times when we've had a particularly leaky train (gotta love historic equipment in the winter) but never had the chance to try the others. I also didn't 100% understand how it worked. Cheers for the explanation, and the other examples.
As a Driver (Engineer) here in Australia I found your explanation fascinating for the different terminology you use there. Apart from the obvious metric measurements of air instead of imperial, we use different terms for what is essentially the same equipment. We use all three methods of braking here you described. All three are referred to as cheating but completely necessary on certain trains.
@@lexx555 the little terminology differences are some of my favorite things... We do the same things, speak the same language, but it feels all wrong... Lol!
@@Hyce777 I know! Its even more strange considering that most of the locomotive components and wagon (freight car) braking equipment we use is from the USA (GE, EMD, Wabtec etc). By the way great video mate.
@@Hyce777 what’s your favourite locomotive that you have run IRL
I only started watching you like three days ago but still I have been waiting for this video to come out. Glad it finally dropped!
I really appreciate you putting out this video, it has helped me gain an better understanding on how air brakes work and how to use them! this will be a big help on train simulator 2022
Love these 10 levels videos! keep up the great work!
As a train driver in Europe I'm glad to get al the way to level 10 with out hearing to much new things. Somethings are slightly different, like level 8 with the valves looking for the speed of the reduction. I don't think they are used here. But I'm only a passenger train driver not freight, and they are at max 700 meteres long so not that we realy need those. And those truck like brakes with the spring we actualy have those here in some loco's and trainsets, but they replace the handbrake.
But a great video, a bit long, but verry good and I like the art style with the paint drawings. It has a charm about it
Cheers! Yeah, this video was intended for folks with less than that understanding so it's good you didn't learn more. Maybe down the road in a future more in-depth video :)
UIC distributors with emergency valves actually exist in Europe, but my gathering is that they are very very rarely used. So far I've only seen them on a few autoracks specifically designed for passenger trains ("Autozug" "Autoslaap" or whatever they're called locally), when they sense a sharp reduction in the brake pipe they keep dumping air until it gets empty enough... a real PITA when doing shunting moves with those (plus they're LOUD)
watching these videos makes me want to revisit the strasburg railroad museum just to see all these on the different trains.
A fascinating explanation of how train air brakes work. I was a Car-Inspector for Amtrak & NYC Transit for most of my working life (now retired) & I can just imagine how inspiring this video would be back when I started out in 1974. When you are actually working on trains you don't always take the time to stop & smell the roses, but when you look back at what you did you get a better understanding & appreciation for how trains work. I hope your videos inspire more young people to consider the interesting field of train car repair, either as a Carman, Electrician, Machinist, etc. With high-speed rail along the horizon there should be many opportunities to get hired onto a railroad or subway system. Keep up the good work Mr. Huber!
Cheers! I imagine you have a lot of good stories. Enjoy retirement :D
Excellent explanation. I am taking up Air Brakes in class now (locomotive engineer training program). This helped so much.
My experiences with HIGH FRICTION COMPOSITION BRAKE SHOES.
I recall the GN testing high friction brakes shoes when I was a GN Brakeman 1960-68. The tests were around Bethel, MN that's about 35 miles North of Mpls. On the GN line from Superior, WI to Minneapolis, MN. I wasn't on the crew but heard that they were testing by going different speeds and even dynamiting the air. Trouble was that testing was being done mid-day in a August heat wave! I haven't seen any testing being done in cold weather that is experienced in Northern States. Ya, coldest as a Brakeman -48f in Cass Lake, MN, and coupling air hose's. You'd grab the near hose with two hands and bend it up into a u-shape. Then grab the far air hose and bend it up waiting for the near air hose to slowly, slowly try to straighten out, guiding the glad hands to a connection. Then I rode the tail end (100 cars) two and a half miles to a joint and walked to the engine. I know about cold weather.
The first year as a Fireman I started on the old DSS&A line Superior, WI to Ewen, MI. We were picking up a car of lumber on the Connersville Spur, that's just east of Thomason Siding. We had a GE U30c, an 800 and was picking the car up with the lite engine. We approached the car and the engine was plowing a large snow pile higher than the coupler. Don Beasley stopped me just short of the car and had me pull away so he could clear the snow away from the couple itself. If you were to try and couple with all that snow you had the chance of blocking the lock block from falling in place. If that happened you would have to remove the knuckle to clear the lock block. I pulled away about a good half car length and stopped. I reached for my coffee bottle and then Don was screaming at me over the radio, the engine was backing up and would crush him if he hadn't seen it to his side vision. That was really scary. SCARY. It was downhill there but I never had a GP 7 or 9 do that. My first impression was that the composition shoe polished the wheel surface so much and the shoe being cold would not provide enough friction to hold. I later found that this was only a small part of the problem in cold weather. Cast Iron shoes leave a lot rougher surface on the wheel and the shoes wear a lot faster. What happens on the road is the shoes get hot when used and trailing thru snow or blowing snow it melts on the shoe and gives it a coating of ice. The next time the brakes are used that ice layer needs to be broken thru. Cast Iron shoes leaving a rougher surface breaks thru faster even with lite applications. (6 pound notch reduction) not so with the composition shoes. I found that in snow conditions a twelve to fifteen pound reduction was the least I felt comfortable with to break through that ice layer.
I worked a 3pm switch engine at Rices Point Yard in Duluth, MN. There was a lot of snow and blowing snow. When I inspected the engine going to work, the brakes told a story. With the repeated application and releases of the brakes, there was a three quarter inch layer of compacted snow/ice on the working surface of the brake shoes. All twelve wheels. ICE BRAKES??? I left the independent brake on full and took a full service reduction on the automatic to increase the cylinder pressure even more to wear the ice away. After that I carried a magnet that I would put on the side of the independent brake handle on engines with composition shoes so the brakes would never fully release in those working conditions.
My last trip as a brakeman on the GN was a real eye opener concerning composition shoes. I was on a taconite train. The lead engines speedometer was off, really off. 32 was about 48 or more. Engineer was from Kelly Lake and I believe unfamiliar working out of Superior as I had never seen or worked with him. Up with empty's, pull thru the loading tipple and return to Allouez Ore Yard unloading shed. Four or five car units with solid drawbars between them and rotary couplers on each end. Usually two hundred fifteen cars. Loading tipple would;d tell you how much was loaded, usually fifteen or sixteen thousand tons, plus you needed to add the weight of the taconite cars. It's starts downhill at Cloquet, MN all the way to Boylston Jct. I don't have a timecard but it's about twenty-five miles. Speed limit on taconite was thirty mph. Going thru Dewey speed was close to an actual speed of 45+ mph. The conductor called and said we had cars on the ground. Engineer started an application. Conductor dumped the air. Leaving Dewey there is a slightly increase downgrade. Speed increased to fifty mph with the train in emergency. The next station is Boylston Jct.. The signal was double red as the Passenger Train headed to Mpls/St. Paul was approaching Boylston Jct. and so were we, except our train wasn't going to stop short of Boylston. This is going to be close. The passenger train made it. The signal changed for us less than an engine length from the signal. When we stopped we had three engines and five taconite cars beyond the junction switch. Less the two minutes from either spearing or head-on collision with the passenger train. I walked the entire taconite train and found four leading axles on four widely separated locations on the ground South of the South rail.
The train went very close to, or did go five miles with the train in emergency.
The taconite cars had roller bearing axles and composition brake shoes.
I had another experience with excess speed with 100 empty freight cars, but with cast iron shoes this time. Speed was forty seconds a mile. That's whole n other story, and ore trains too.
I had some fun and games with trains, ones with cast iron brake shoes and forty foot box cars filled with grain that is. Leaving Glenwood, MN the first stop for us was at Brooten, MN. That's where we needed to line a switch entering the Brooten Line to Superior, WI. Track speed was 40mph. By the mile board at 40. A lite application kicking off the head end brakes to keep everything stretched. Then seeing how fast I could go over the main street crossing and still stop for the junction switch. At the road crossing increase to a full service reduction and stop in about 700 feet for the switch. After many trips, well, at 26 I put the lead wheel of the engine on the points. That was the end of that shit. There is the saying “Stop short, NO Guts. Run by, POOR JUDGEMENT”. I found that slowing for the head man to get the switch without stopping was actually faster. Same with the hind-end lining the switch back. On many a 200 mile trip the first stop was at the yarding track in Superior. Jack Peterson hogheaddotnet
I love reading these stories of yours Jack! Would be great to do an episode of just you telling train stories :)
A very good and simple to understand for an air brake application
Fantastic video. Very informative. Please continue to make these.
WORLDWIDE TRAIN BRAKE SYSTEMS
First principles of any railway train brake system is that it must be "Fail Safe". In other words if something goes wrong, such as the trains couplings break, both parts of the train MUST still be able to make an emergency stop. So must automatically apply on ALL vehicles, to bring both parts to a safe halt. Virtually all train brake systems world wide fall into two categories namely Vacuum or Air brake. Although many steam locomotives also had steam brakes for use SOLELY on the locomotive. (Used when a locomotive is moving by itself).
BASIC VACUUM BRAKE SYSTEM.
With Vacuum brakes the air is removed from the train brake pipe, by an ejector (sucking pump) to RELEASE the brakes. If the train breaks in two, then the pipe between those vehicles breaks and atmospheric air naturally rushes into the pipe, destroying the vacuum and automatically applying the brakes on all vehicles. In normal use the driver can graduate slowly the amount of air allowed into the pipe, to bring the train to a controlled and gentle halt.
BASIC AIR BRAKE SYSTEM
Basically a reversed vacuum system, whereby Pressurised air is needed to RELEASE the brakes, & provided by an air pump. If the train breaks in two then obviously the pressurised air rushes out, so applying the brakes on all vehicles. In normal use the driver can graduate the release of the air pressure slowly, so all the brake blocks on all vehicles begin gently rubbing on the wheels to bring the train to a nice smooth and gentle halt.
LIMITATIONS OF THE SYSTEMS ABOVE.
The Downside of both the Vacuum & Air brake systems as explained above. Is that in normal use, the Vacuum or Air pressure is controlled from the brake handle in the locomotive cab. So it takes time for the vacuum or air pressure to change, as the effect of this change has to pass along the whole of the train from front to rear. This slows down a trains ability to stop quickly.
As a result of the DOWNSIDE of the above systems, certain alternatives are possible. The British Great Western Railway for example used a higher level of vacuum than the other railways of Britain, so allowing a somewhat quicker reaction by the trains brakes to the drivers use of the brake handle, and in addition "rapid reaction" release valves on each passenger vehicle. (This was not applied on freight vehicles).
With Air Brakes, which were NOT common in Britain or Spain/Portugal in the steam era, a Major change came with the arrival of Diesel & Electric locomotives. A Dual pipe system was introduced, where you have in addition to the "Brake Pipe", a second pipe known as the "Main reservoir pipe". This allows the Air brake system to be used as previously described using the brake pipe. But the addition of the 2nd "Main Reservoir" pipe allows pressurised air cylinders on each vehicle to be constantly kept charged with air pressure. When the air brake is used in normal use, by releasing air pressure to slow a train down for a sharp curve for example. Then when the brake is released, it can recharge direct from the air reservoir tanks, so as not to waste time waiting for the brakes too release as with the single brake pipe system.
Railways in Britain can be extremely busy with trains every couple of minutes, so the dual pipe system is very beneficial, in reducing delays to trains.
The modern Air brake system, can be taken yet further, if you also have an electrical supply along the whole of the train. Such as with Multiple Unit (Diesel or Electric) type passenger trains, which are common all over Europe. In this case the air pressure valves on each vehicle are all controlled by an electric relay so that ALL vehicles in the train begin braking simultaneously, and do not have to wait for the air pressure change to feed slowly along the trains brake pipe. This type of electric Air brake is known as EPB (Electro-Pneumatic Brake) in Britain.
An example of the EPB brakes use (first introduced in Britain in 1951), is that I was able to stop a 12 car electric train (3x 4CEP/BEP units), around 800ft long and weighing roughly 450 tons +31 tons of passengers, from 60mph in its own length of 800ft. Using a normal instant full brake application (Not Emergency application). For ANY train this is extremely rapid deceleration. Even though this was a commuter express with a Restaurant car, the train was brought to a smooth halt, and not a drop of tea was spilt in the catering vehicle. Indeed having driven trains in many parts of the World, I have never found any other brake system anywhere in the world capable of such rapid deceleration, not even Metro type trains !!!
Bake Mania 😝
Brilliant, brilliant, comment. Cheers for the info!
Thank you for the reply on UK trains.
The old UK Basic Vacuum Brake system
When you connect your engine to a train thats brakes are already applied using the vacuum system.
The engine then pulls the same vacuum in the system and all the brakes will come off. (except the guards hand brake)
The guard will check he is getting the correct vacuum at his end of the train.
If correct then the vacuum is destroyed and the guard will then walk the length of the train to confirm all brakes have gone on fully.
If the engine is unable to pull the vacuum, the train must be taken out of service.
The train can still be moved by first walking the train and pulling a cord connected to every brake cylinder. This will equalise the air pressure / vacuum in each cylinder. This would also be done to change from an British Great Western Railway engine 25" mercury system to a standard 21" system.
@@ryanknox3522 The train airbrake system in Britain is today, a two pipe system, with a Main Reservoir pipe in addition to a Brake pipe. This allows rapid recharging of the brake pipe by the main reservoir pipe, (especially helpful on passenger trains). Because a pressurised air supply is held in air tanks on all vehicles. When air pressure is released from the Brake pipe when the driver uses the brake handle in the locomotive, the falling air pressure begins to apply brake blocks to the wheels, retarding the train. When the brake handle is released, air flows from the vehicle reservoir cylinders back into the Brake pipe, releasing the brakes far more quickly than using a single pipe system as found in the USA & Europe.
There is also an even more sophisticated air brake system available from 1951 on electric passenger trains, where electric wires along the train are used to control the Brake pipe, reservoirs & main reservoir pipe automatically to apply and release the brakes simultaneously on all vehicles, therefore dramatically reducing braking distance. This system was known as the Electro Pneumatic Brake (EPB).
More modern attempts to replace parts of the air pipe system with more electronics, and replace brake blocks with disc brakes, have unfortunately led to retrograde steps in actual braking performance, especially in adverse weather conditions. The most notorious being the BR 1980's "3 Step brake" (an electronically controlled air brake with a lack of versatility of the air pressure required), which should have been banned, as dangerous.
So I have never found anything as good as the EPB brake for stopping passenger trains. Freight is a totally different issue, as braking becomes a lot harder & requires more skill, especially when you have two 45 tonne wagons full of commercial explosives included in the train !!!!
The engineering, complexity and intelligence of rail design and use is hard to comprehend. The deeper you look, the deeper it gets. Thank you for all of these videos! Any topic involved in railroads is a great idea for content like this!!
It's all refining over decades and decades of learned lessons. Lessons usually learned the hard way (damage to either property or people).
Fantastic video! Really simplifies everything without really skipping over amt of the important information. Thanks!
It's nice to see another narrow gauge railroader tell people how all of these things work as a teenager who volunteers at a narrow gauge railroad this is very helpful for me learning stuff that I don't know especially when I get to become a fireman or an engineer because I'm only 6 years away from getting my degree and if you're wondering what the narrow gauge railroad is it's Midwest Central railroad
Hyce, thank you. This is basically a UA-cam tutorial for building a steam locomotive
I’m not even joking. Imma do it.
These 101 videos will be superb in helping me in my future job as train crew for the UP. We all start as brakemen in the train crew trade, so this primer will be highly useful for that.
Most people are visual learners so your pictures work well, combined with the knowledge you have on the subject you're talking about I think you do a fantastic job. Great work!
I see you are a Benny Hill fan.👍👍👍
George Westinghouse was a genius
This is incredibly informative and explained perfectly. Thank you for this video and btw, the drawings were spot on.
Very good. I've been playing train sim since 2001 (MSTS) and I understand the brakes from watching how they behave, but this helps with some of the mechanical details.
Great just great video! Im loving these types of videos!
The greatest possible pressure difference in a vacuum pipe is 14.7 psi i.e. one atmosphere. The diameter must be larger to deliver the same power as a 90 psi system.
Thank you for this Video, I learned quite a few things.
literally cleared my confusion and clearified more in depth of how brakes work on a train. thinking about becoming a mechanic for a railroad.
I think you've answered one of the mysteries of my childhood. I lived along a preserved railway and a tiny 0-4-0 I often rode behind (and sometimes in) had a tiny diesel engine on a bracket they'd added to the back of the cab. It never occurred to me all this time, but now I realise it was actually an air compressor for the brake lines. I don't know why they'd need it but I have a few guesses- original equipment was too weak, incompatible for some reason, or needing repair perhaps.
or it was an ancient engine with no air brake equipment fitted or vacuum brakes
the best explanation I have ever heard about railroad air brakes. thank you.
Interesting story about the accidental dump save. I have done something similar on a 24RL on a GE 23 tonner.
The engine had just come back from a big overhaul of the electrical system and just had the 24RL put in, prior it was 6BL or something similar.
I was coming down the hill and was making a small 8-10 pound reduction, going in small hits because the hill is a gradual decline. That day we found out the dump bump had been ground down so low, you can't even feel the difference from the service position.
Realizing it had dumped, I immediately put it into lap and managed to save the MR and only dumped about 30 pounds from the BP. Moved it to release, and after a small jolt and a short stop, kept going.
I'm not the only one! Haha. I've dealt with "modified" bumps before... never fun. I wish I knew more about 24RL, it seems neat. I've never really interfaced with it.
@@Hyce777 It's a lot of fun. I love the non-self lapping stands, you have so much more control. It takes a decent amount of skill to master charging the trainline without overcharging, but it's super rewarding. It's not all that different to work with than the 6 other than pressure maintaining... unless you work in the mechanical department!
@@PowerTrain611 Lol! good to know. I just recall our machinists at BNSF needing to get the SD9 in the picture to pass an air test to tow it out for sale and no one knew 24RL... quite complex on the mechanical end, good to know operationally it's not too different :D
You illustrations are impecable ;)
Feel like I’m getting trained for an actual job by listening to Hyce.
I really enjoy your Railroading 101 videos! I have volunteered as rear brakeman on the Sumpter Valley R.R. in E. Oregon.
Very cool!
I'm not going to go through nearly 300 comments to see what all was mentioned. I was a CSX engineer for eight years nearly 14 years ago and went through engine school in 2000 when it was in Cumberland, MD. Air brakes and air brake theory at that time was an entire WEEK of the month of classroom instruction. That is how important this is. He didn't even get into the difference between passenger brakes and freight brakes. Passenger air allows for a gradual release of the air, while freight air is either applied or fully released. Then there is "blended" braking used by Amtrak and commuter authorities on modern locomotives, which combines air and dynamic braking. I never used it, so I can't explain it, but it's essentially single-handle braking that seamlessly uses both air and dynamic brakes in the optimal combination for conditions. Another aspect of air brakes and how they work is the difference between the flow rates of normal or "service" air flow and emergency air flow. The brake valves on the cars are designed to know how fast the air is flowing past them and use that to decide when to apply the emergency brakes. Service air flows at about 400 ft./sec. and emergency air flows at about 900 ft./sec. (Which means on a 10,000 ft. train there would be over a 10 second delay between the front and the rear cars in putting the consist into emergency, which could cause a derailment. One reason why "The Big Hole" is something not to be used carelessly. Modern End of Train devices can be triggered to dump their air valve, so most engineers are taught to do that at the same time they hit the "Oh, Sh*t" handle.) So, say the conductor is adding a cut of cars to a train and turning the air into the cars and moves the angle cock a little too fast and the air from the cars already in the train starts flowing faster than normal into the new cars, the brakes might think they are supposed to go into emergency and dump. Common rookie conductor mistake. Also, the small air reservoirs on each car are divided into two sections, a service air and an emergency air section, which is how the emergency air gets applied to the brakes throughout the train so fast. Everything is charged from the main brake pipe hose. Freight air is 90 psi, passenger air is 110 psi, switching air is 80 psi, and ground air (which is a very important thing when it comes to brake tests) is 70 psi. The reason that ground air and switching air are lower is so when the cars are added to a train they will match the "gradient" of the air brake profile of the rest of the train. Most trains of any length do not maintain 90 psi over their entire length. CSX rules allowed for a 15 lb. difference in pressure between the front and rear to pass an air brake test, meaning you could pass the test with a reading of 75 psi on the rear with a full release on the head end. Bear in mind that this is also affected by things like outside air temperature. The colder the weather, the harder it is to maintain train line pressure over the length of a long train. I don't know how the Class Is are able to operate 15,000 ft. trains in January in the North, especially if there isn't a DPU either in the middle or on the rear of the train to add air pressure? I had enough trouble sometimes with trains under 10,000 ft. in Winter.
Some mainline excursion steam locomotives do use 26L freight brakes. I know for sure that Nickel Plate 765 does and the Ohio Central steam locomotives that ran regular excursion service (1293 and 6325) did. I believe N&W 611 might also. I've been told that UP 844 and 4014 use older types of steam locomotive brakes. Most tourist railroads use freight air and not passenger air setups, so no gradual release.
Man, the amount of brilliant comments coming in lately on this video from folks like yourself is fantastic. Great info in here, some of which i knew, some of which i didn't. Appreciate your insight and adds! Yeah, there's a reason real airbrake classes are so long. Hopefully with your knowledge you agree that this was an OK first look for folks who don't know it at all! Haha.
@@Hyce777 Yeah, most fans really don't care about the detail. I put together a program on railroad operating practices for fans at what I thought was a basic level and it pretty much was a snoozer. So, your attempt is probably about right for most fans. The most important things any engineer has to know are 1) the grades of whatever territory they are operating over, and 2) how to safely stop whatever size and weight of train they are operating. The thing that surprised me most about becoming an engineer was how different the reality of operating is from what a fan thinks it is. And that is too long an explanation for here.
I never even thought of air temperature and the resulting effect on air density as being another bug-a-boo in train brake operation. Thanks for the real-world info.
@@fiddlyphuk6414 Not only that, but when you compress air you heat it and wring the moisture out of it as it cools back down. Which is why the pipes from the compressor to the main reservoir curve around - to cool the newly compressed air. It's also why there are "spitter" valves on the air systems of locomotives, to continuously drain the moisture from the tanks. Some railroads, like CSX, also use air dryers that kind of look like small air compressors on the train line to further dry out the air before it goes back through the train. Moisture in the air line can freeze the brake line in the winter and either cause damage or prevent the brakes from working properly. In the "old days" a lot of conductors used to carry gas dryer with them, which is alcohol-based, and separates out water when poured into the brake line at a hose, but it also will ruin rubber brake hoses and gaskets over time, so the company doesn't want them to do that.
Before DPU became common I know the Canadian class 1s had compressor cars to help maintain the pressure in winter. I've never seen a good description of how they would work but I assume it would been limited to how much air it could add to the system all at once and have a valve similar to what was on the cars with the difference being when the air pipe was being charged or held it would try to hold pressure. A reduction would stop the maintaining process until a release/charge was sensed. Anyone have info on those?
I was a Carman for a little over 3 years on a modern freight railroad this is a great history lesson and I wish I could have had it when I trained as a Carman. It simplified what the brakes are doing and why.
I like what you did with the steam, and I like what you did here. I can now play on train sim and understand better what I'm doing.
Thanks for the great, easy to understand and well taught video!
A video about train airbrakes is the last place I expected to find extreme vocal fry. Thank goodness there are subtitles.
Yeah, unfortunately in this era of my channel I was having some serious audio codec issues that plagued me for a while. Since been fixed. Turns out if you spend too much money on audio gear, it starts to cause problems instead of fixing them...
Glad to see this since I found you through a detail valley video I think. Watch a lot of videos where they don’t understand the brakes at all. I think it was once said I can do with 10lbs reduction anything you can do with a full application. So I try to plan my moves two or three moves ahead. Would love to run a real train but I only got to watch as a kid.
Really interesting subject. Maybe in one of your future videos, you can explain the different scenarios of operating a train when you apply your different brake levels. # of cars, grade, speed, curve, type of load, etc.
Very nice video Hyce.
And since you tried the Zeibach's Couplers mod, I suggest you and kAN should try the Derail Valley Multiplayer mod. Veri fun
Excellent so many thanks for sharing your expert knowledge. I’m really enjoying your videos-recently discovered them. You’ve got an eager student!
Cheers Patrick!
Thanks for posting this tutorial. I may go work for a tourist road after I retire from my "real" job, and they run F7 and GP9 diesels with 24RL stands (one switcher has 6 air, but it probably will never run again). I have had a good understanding for years HOW automatic air worked, but this really enlightened me WHY it works. Perhaps sometime you could discuss engines with pressure maintaining? The aforementioned road has one 1950 vintage F7 that lacks both dynamic brakes and pressure maintaining; the engineer has to work the air like it is steam engine days!
Glad you enjoyed it! Yeah, pressure maintaining would be a good topic. I'd need to read up on it myself, never had the pleasure of really getting to run anything with it, haha. I've always thought of retiring to the tourist ops myself :)
@@Hyce777 if you do, it's also worth noting that it is possible to trick those older brake valves into pressure maintaining by using the regulating or feed valve, this unapproved technique is of course referred to as "feed valve braking". It can also come in handy on the 26 or 30 systems if pressure maintaining fails (usually from a leak somewhere on the equalizing reservoir piping) and the brake valve does not have both freight and passenger settings (switching to passenger usually makes it work again).
Electronic brake valves won't let you change the settings or feed valve pressure while the train is moving, but I've never seen pressure maintaining fail on any of them.
Very well explained! I Agree, these videos should be required training for both Conductors and Engineers just coming into service. Great job!
Yes.. i needed this also I'll prolly post my questions on this vid once I finish watching
Awesome explanation!!
Maybe do a video on whistle signals? Idk, love your videos though, keep up the great work!
So you can use a cross compound pump to make air at higher pressure than the steam. You just need a larger steam piston than an air piston. Pressure is force/area after all.
Air over hydraulic pumps use this principal to get pretty crazy pressures from 100 psi air.
I miss level 11: How an automatic brake of simple concept (or from the early days, the ones with simple comparision between reservoir and train pipe) can be exhausted by multiple applications of brakes without appropriate re-charging in between applications. And how the brakes can fail if left in lap due to slowly discharging the train pipe and brake reservoirs over time without brake application.
It's about the volume of air required, and the fact that steam air compressors were not the most efficient beasts around, and as well the charge rate for the reservoirs is pretty slow. From empty, it takes about 5 minutes to completely charge a small train even - so, if you use enough air setting, releasing, setting, releasing, etc. - you can lose sufficient capacity in the reservoirs fast enough that you're using much more than the air compressor can keep up with, and either you lose braking power from the reservoirs being empty or you lose braking power because your main reservoir cannot keep up with demand, which leads to the same. It takes a lot to get there though, and this is controlled by the book of Air Brake and Train Handling rules.
There's a rule with non-self lapping brake valves that you can't have more than 5 PSI / minute leak (different by RR rules as well, I believe 5 is the maximum though) to mitigate any other failures. If you've got a big enough leak at the right spot in your brake pipe, you can't charge the rest of the train.
@@Hyce777 +Brakes according to the FRA are required to remain set for five minutes. Most when set out I've seen them still set a week later. The problem with the brake pipe pressure dropping below the equalization pressure is that an emergency application is no longer available. Emergency applications provide for 20% higher brake cylinder pressure. Jack Peterson hogheaddotnet
Really enjoying the series. I'd like to see how they would release if there's enough information on that topic.
Also as a side note, i can hear quite a bit of popping from time to time in the audio
Aware of the popping.... Ugh. And yeah, there's more detail but we didn't get into it in this video.
@@Hyce777 Hi there. Friend from the museum I volunteer at sent me this video and I plan on going over this in depth as I am always looking to learn. Ping me if you want help with the audio. Either we can work on preventing in the first place, or removing it post-production.
This is very informative. Actually I was curious how train breaks works while playing Train Simulator. Thanks
Great video as all ways Mark.
Hyce, this was a great informative video! I was an electrician and did PTC for UP at the Roseville shop, until they extended the deadline, and laid us all off! I’m always up to help if you have any questions about the electrical side.
Hey thanks Ted! You did the real wizardry in the loco shop... I never really did get a good handle on the electrical side.
@@Hyce777 that’s the fun stuff!
Yesss! Air brakes! Thanks hyce!
I find it interesting that the way the brake systems in the train I saw at a storage house and these you are explaining, the brakes work differently but they are connecting-compatible.
The one I was shown, the brakes, there's no reservoir, they work closely to how trucks work (with a spring to apply by default) and they have a brake disengage too.
The disengage works by rotating a flywheel a few times to mechanically overcome the spring which engages the brakes. The flywheel then requires setting a fail-safe 1-way, position-evident pin to lock in the open position. Note: In this design, the brake wheel cannot be used to pull the brakes.
The fail-safe is that if a train is connected and it pressurizes beyond the current brake opening (which will happen when applying full brake disengage), the pin loosens and resets.
Do note I'm not from USA or even America.
Great stuff here! Subscribed!
In the UK we have an additional pipe. The train pipe is red and the resevoir pipe is yellow. The resevoir pipe keeps each cars resevoir toped up which gives a quicker release time.
ONn the HIGH sPEED TRAin, with a service speed of 125 MPH and it was found that it took too long for the train pipe to dump air. This problem was solved with an electrical actuator in the rear loo. The HST has a loco at each end of 7 to 9 passenger coache. When the driver moves the brake handle an electrical sihnal is sent to the rear loco so a brake valve follos the lead loco and the air is exhausting from the train pipe from both ends to give a shorter stoping distance
Shoot this is good stuff ive got to go back a few times to take it in..excellent presentation. Hope you can explain how throttles are co ordinated when more than one locomotive. Subbing
Your lecture is better than that of some schoolteachers. Today, October 24, 2022, I subscribed to your channel. Happy Railroading!
Cheers mate!
@@Hyce777 Thank you for tapping or typing to me!🙂
Anyone who thinks that this is long video should consider that airbrakes in trucks(at least) is a level of licensing all on it's own
The fact we made it through this video without the name 'Westinghouse' being said is quite fantastic to me!
Was trying to give an overall context, and not muddy things of brands... westinghouse, new york airbrake, wabco, wabtec... lol
Except that it was Westinghouse who first invented the concept of the train airbrake. Not sure where there is a problem with that. Yes maybe there are other companies now that have since improved upon his original designs but the functionality of the design still originates with him.
@@Robotechnology101 That's fair, I certainly could have mentioned them in that context, but I was trying to just keep it to a functional base-level overview. Certainly would've been a good nod, but I don't think necessary.
This is the same man who had Westinghouse Electric.He was a rival of Edison.There is an interesting DVD about Westinghouse.
4:35 - in the 19th century the usual working pressure on New Zealand steam locomotives was 130 lbs PSI. This later went up to 160 lbs PSI and I think that must have been when we adopted the Westinghouse air brake system which was introduced across the network in 1900-03. The higher pressure being necessary to run the brake pumps and create the greater pressure required for the braking system.
+1 for not being an AI bot that created another one of the 100 videos on this subject. Thank you.
You were right this video was very helpful. I hope to see more back of the napkin learning videos. Maybe one on the different types of steam locomotive driving gear?
That's a common request! I am going to have do some more reading. I know a fair bit about Stephenson, Walschaertz, and Baker, but not the others...
A very good explanation of something I did not understand. One error is the statement that air pressure cannot be higher than steam pressure. As long as the steam piston is larger than the air piston the air pressure will be higher.
Yup, I goofed that one :P
Nicely done! I finally get it.
So I'm a mechanic who works on semi truck air brakes. (Which were derived from train ones I believe). so it was relatively easy for me to understand.
Excellent job!
let us... everyone here, let us kickstart the project so to get Hyce's knowledge presented in a proper way, with animations and graphics and all.
I have ridden the Coumbres and Toultec several times. A fun trip including a buffet lunch. Try it, you will have a blast.
It's the one to do!
Hi,
Very goed explained this topic.
Greetings from European train driver.
Very informative, I never knew the air brakes on a train was that complicated even with 2 lifelong railroad men in the family.
I am a trucker and honestly believe that we have the simpler, more reliable and better air brake system.
Certainly so! It's a lot easier to have a better system when you're talking a trailer or a few vs. several hundred, haha. Cheers :)
The basic trouble with train air brakes is railcars need to be able to roll when not hooked up to air, so they can't just have a "brakes are ALWAYS applied without air pressure" system.
30:03 reminds me of how in a dual-control military aircraft there is the convention of "shake to take, pump to pass" where the need to take or cede control can be communicated only through the coupled controls, if need be.
Similar for sure! That's cool.
fantastic video
Great video. Brings up a lot more questions then it answers, lol.
That is the fun of airbrakes... lol. What questions do you have?
very nice video, I learned a lot.
Interesting description. Trying to keep it as simple as possible is always a problem. One of the easiest methods for describing the automatic air function was the idea equalized air pressure on each side of a piston and how reduction of pressure on one side moves the piston to perform a function. When the pressure is equalized, the piston stops and slightly reverse moves to stop the function. The use of rubber diaphragms has made for a more sensitive operation of what ever valve diaphragms are used in. Also, the timing involved in charging, reducing train line pressure.
From front to rear, timing is involved. For example, when stopping a steam powered locomotive on a freight train, going up an ascending grade to take water. Slack most likely will have to be taken to get the train started. After taking slack, the release time for K-2 vs AB was about 2.5 to 1.5 seconds to start each car to release. The trick was to start the pull about the time the release got to the rear end. But before the rear end would run out and possible cause a break in two. Another area that is not dealt with these days is the use of retainers when braking on steep down grades with long mileage. Anyone can turn up a retainer, but the proper use of the automatic brake valve without the pressure maintaining feature to prevent insufficient recharge of the auxiliary reservoirs is another story. Yes, knowing the air is an interesting subject.
Sounds like you've pulled away with one or two trains yourself based on that description - thanks for the comment :)
I love your graphics my friend.
The Bessemer & Lake Erie RR had a large number of open top hopper cars that were used for bulk mineral commodities - those cars had double clasp brakes - shoes on the inside and outside of each wheel. When my railroad hauled those cars they were generally referred to as 'Rattlers' as the made about double the noise as the more normal single clasp brakes used on most freight cars. Secondly, there is no such thing as a 'partial release' of freight car brakes, once applied they can be applied harder, but the brake pressure cannot be reduced except to be totally released. PTC is more like level 20 or 30 in your scheme.
Oh, good to know. I am going to need to consult some folks about the early K valves because I was pretty sure you could partially exhaust things. Wouldn't be surprised if I was taught wrong though! And, yeah, PTC is probably a higher level, but I thought it would be good to tie in my current experience into these things (I am a signal engineer by trade anymore).
Hyce excellent work. I was a machinist locomotive air brake mechanic at BN Northtown for 35 years (started on GN in '69) . I installed 26 L on the ATSF 2926 steam locomotive in Albuquerque where you could contact me. Some would call me an expert but I learned some things from you. I would be glad to help you.
Northtown! Awesome. I worked at Interbay for a few years. And - very cool, would be great to talk with you about the 26L you installed on the big gal.
great explanations. getting into modeling and working on boxcar detail. what is an AB valve and how does it work? thank you.
I might be wrong because it's been a while since I was a railroader, but when making a brake pipe reduction from 90 to 80 pounds, the pressure of the air acting on the brake pistons on the cars isn't 10 PSI. It's closer to 30 PSI. One pound off the brake pipe equates to the control valve admitting about 3 pounds of air to the piston--a roughly 3x multiplier. I forget the technical reason but that is why a 30 lb reduction is about the most you can go (vs. setting a 50 or 60 pound reduction, for example), because you're setting 100% of the 90 lbs of air in the cars' service reservoirs.
3X might be wrong. I don't know the exact term to search for to find out what I'm thinking of. At any rate the idea is that a BP reduction of 10 lbs correlates to a higher pressure of air admitted to the brake piston, and that's why you can't set the automatic below 60-something pounds.
You're correct, and I've been too far away from my car equipment manuals to know the exact number myself. A lot of the NG we didn't worry about that because with the old F valves, and light coaches, you could get things sliding at like a 12-13 PSI reduction... so we never got that far. But yeah, the pressure is actually higher.
The reason I heard a while ago is a bit different. The brake cylinder is about 2.5 times smaller than the reservoir. That means that, for example, a 5 lb reduction has to squeeze into the smaller cylinder and is thus more pressurized, and ends up as 12.5 lbs. That wouldn't explain why you can only get up to about 30 lbs reduction, though, since the reservoir would still have 85 lbs in it.
@@BandanRRChannel Bingo...
@@BandanRRChannel You start sliding the wheels before you run out of air :D
I believe that the use of vacuum brakes in Britain was because our trains are much smaller than in the US. (As in, less tall and less wide, not just shorter.) On a steam locomotive, you can use a vacuum ejector, which is small and has no moving parts. Air compressors are much bulkier and there generally wasn't room for them on UK steam locomotives. Vacuum brakes were fine for the weight of trains we were running and, hey, many low-speed freight trains had no automatic brakes at all -- just the locomotive brakes, and a brake van at the back. If they needed to go down a steep hill, they'd stop and make partial handbrake applications.
When diesel locomotives came along, they had to use mechanical vacuum pumps, which have no advantage over air compressors, so the general advantages of air brakes won out, eventually.
Not only does condensate (AKA 'water') not compress, it also freezes. Frozen brake valves even partway down a consist, spell disaster.
Good point!
2:02 I was going to suggest MSPaint, but I realized your hand drawing is totally fine.
Proceed without concern nor shame!